TWI725578B - Gate modulation with inductor - Google Patents

Abstract

A sensor includes a photodiode disposed in a semiconductor material to receive light and convert the light into charge, and a first floating diffusion coupled to the photodiode to receive the charge. A second floating diffusion is coupled to the photodiode to receive the charge, and a first transfer transistor is coupled to transfer the charge from the photodiode into the first floating diffusion. A second transfer transistor is coupled to transfer the charge from the photodiode into the second floating diffusion, and an inductor is coupled between a first gate terminal of the first transfer transistor and a second gate terminal of the second transfer transistor. The inductor, the first gate terminal, and the second gate terminal form a resonant circuit.

Description

Gate modulation with inductor

The present invention generally relates to electronic devices, and specifically (but not exclusively) relates to image sensors.

As the popularity of 3D applications continues to grow in fields such as imaging, movies, games, computers, user interfaces, facial recognition, object recognition, augmented reality, etc., interest in three-dimensional (3D) cameras is increasing. A typical passive way to create 3D images is to use multiple cameras to capture three-dimensional images or multiple images. Using 3D images, you can triangulate objects in the image to create a 3D image. One disadvantage of this triangulation technique is that it is difficult to use a small device to create a 3D image, because there must be a minimum separation distance between the cameras in order to create a 3D image. In addition, this technology is very complicated, and therefore requires a large amount of computer processing power in order to create 3D images in real time.

For applications that require real-time acquisition of 3D images, an active depth imaging system based on time-of-flight measurement is sometimes used. Time-of-flight cameras usually use a light source that guides light to an object, a sensor that detects light reflected from the object, and a process that calculates the distance to the object based on the round trip time it takes for the light to travel to and from the object. unit.

One of the ongoing challenges of obtaining 3D images is to balance the expected performance parameters of the time-of-flight camera with the physical size and power constraints of the system. For example, for imaging far and near objects The electrical requirements of the time-of-flight system of the software may vary greatly. These challenges are caused by external parameters (for example, the desired camera frame rate, depth resolution, and lateral resolution) and inherent parameters (for example, the quantum efficiency of the sensor, fill factor, jitter, and noise) more complicated.

100: Time of Flight System

102: light source

104: emitted light

110: Reflected light

116: lens

120: multiple pixels

122: the first pixel

126: Controller

130: Object

200A: TOF sensor/circuit

200B: Circuit

203: photodiode

205: The first transfer transistor

207: The second transfer transistor

209: The first floating diffusion

211: The second floating diffusion

213: Inductor

C(OX1): Capacitor

C(OX2): Capacitor

C1: Capacitance

C2: Capacitance

f _lens : focal length

L: inductance

Non-limiting and non-exhaustive examples of the present invention are described with reference to the following drawings, in which like reference numerals refer to similar parts throughout the various views, unless otherwise shown.

FIG. 1 is a diagram showing an example of a time-of-flight (TOF) sensor according to the teachings of the present invention.

2A shows an exemplary circuit diagram of a portion of the TOF sensor of FIG. 1 according to the teachings of the present invention.

FIG. 2B shows an example schematic diagram of a portion of the circuit diagram of FIG. 2A according to the teachings of the present invention.

FIG. 2C shows an exemplary schematic diagram of the inductor of FIG. 2B according to the teachings of the present invention.

Corresponding reference characters indicate corresponding components throughout the several views in the figures. Those familiar with the art should understand that the elements in the figures are drawn for simplicity and clarity, and the elements are not necessarily drawn to scale. For example, the size of some elements in the figures may be exaggerated relative to other elements to help improve the understanding of various embodiments of the present invention. Moreover, in order to understand these various embodiments of the present invention in a better way, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are generally not depicted.

This article describes the systems, equipment, and methods used for gate modulation with inductors Instance. In the following description, many specific details are stated in order to provide an exhaustive understanding of the examples. However, those familiar with the relevant technology should realize that one or more of the specific details may not be used or other methods, components, materials, etc. may be used to practice the technology described herein. In other cases, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to "one example" or "one embodiment" means that a particular feature, structure, or characteristic described in combination with the example is included in at least one example of the present invention. Therefore, the phrases "in one example" or "in one embodiment" appearing in multiple places throughout this specification do not necessarily all refer to the same example. In addition, specific features, structures, or characteristics in one or more examples can be combined in any suitable manner.

Some imaging time-of-flight (iTOF) sensors are fully modulated in the device with frequencies ranging from 10 MHz to several 100 MHz. Sensor technology can use gate modulation to transfer charge from the photodiode to the floating diffusion. Some sensors can use gate modulation to accelerate charge transfer within the photodiode when the photodiode is large. However, gate modulation consumes a lot of power, especially when the gate capacitance is large, the gate modulation speed is high, and/or the gate modulation voltage swings large.

As will be shown, an example circuit according to the teachings of the present invention includes two gates modulated at a higher frequency. When one gate is closed, the other gate is closed. The inductor is coupled in series between the two gates and utilizes LC oscillation (ie, resonant circuit) to recycle the power of the gate capacitance when the gates are turned on and off. Therefore, in some instances, it is helpful to reduce the resistance in the LC oscillator to improve the efficiency. Using pixel-level hybrid keys, flexibility can be used for special designs and procedures to reduce the resistance of the metal wires proposed in some examples.

The embodiments discussed above and other embodiments will be further detailed below, because they are related to the figures.

FIG. 1 is a diagram showing an example of a time-of-flight system 100 according to the teachings of the present invention. The time-of-flight system 100 includes a light source 102, a lens 116, a plurality of pixels 120 (including a first pixel 122), and a controller 126 (which includes a control circuit, a memory, a counter device, etc.). The controller 126 is coupled to the light source 102 and a plurality of pixels 120 (including the first pixel 122). A plurality of pixels 120 are positioned at a focal length f _lens from the lens 116. As shown in the example, the light source 102 and the lens 116 are positioned at a distance L from the object 130. It should be understood that FIG. 1 is not drawn to scale, and in one example, the focal length f _{lens is} much smaller than the distance L between the lens 116 and the object 130. Therefore, it should be understood that, for the purpose of the present invention, according to the teachings of the present invention, for the purpose of flight time measurement, the distance L and the distance L+focal length f _{lens are} substantially equal. As shown, the plurality of pixels 120 and the controller 126 are represented as separate components. However, it should be understood that the plurality of pixels 120 and the controller 126 can all be integrated on the same stacked chip sensor and may also include a time-to-digital converter (or a plurality of time-to-digital converters, where each pixel (Associated with one of a plurality of time-to-digital converters). In other examples, the plurality of pixels 120 and the controller 126 can be integrated on a non-stacked planar sensor. It should also be understood that each pixel (or even each SPAD) may have a corresponding memory for storing one of the digital bits or signals used to count the detected photons.

The time-of-flight system 100 may be a 3D camera, which is based on the time-of-flight measurement and calculation performed by a plurality of pixels 120 to image depth information of a scene (for example, the object 130). Each pixel in the plurality of pixels 120 determines the depth information of a corresponding part of the object 130 so that a 3D image of the object 130 can be generated. The depth information is determined by measuring the round trip time of the light propagating from the light source 102 to the object 130 and back to the time-of-flight system 100. As shown, the light source 102 (for example, a vertical cavity surface emitting laser that can emit visible, infrared or ultraviolet light) is configured to emit light 104 to an object 130 a distance L away. Then, the emitted light 104 is reflected from the object 130 as the reflected light 110, and a part of the reflected light 110 propagates toward the time-of-flight system 100 a distance L away and enters It shines on a plurality of pixels 120 as light. Each pixel in the plurality of pixels 120 (such as the first pixel 122) includes a photodiode (such as one or more single photon burst diodes) that detects image light and converts the image light into electrical signals (such as electric charges). Body (SPAD)).

As shown in the depicted example, the round trip time of the pulse of emitted light 104 propagating from the light source 102 to the object 130 and back to the plurality of pixels 120 can be used to determine the distance L using the following relationship in the following equations (1) and (2):

其中c係光速，其大約等於3×10⁸m/s，且T_TOF對應於往返時間，其係光之脈衝行進至圖1中所展示之物件及自該物件行進所花費之時間量。因此，一旦已知往返時間，可計算距離L且其隨後被用於判定物件130之深度資訊。控制器126耦合至複數個像素120(包含第一像素122，其可耦合至讀出電路以讀出電荷及將該電荷轉換至指示電荷之資料)及光源102，且包含邏輯，該邏輯當被執行時致使飛行時間系統100執行用於判定往返時間之操作。邏輯可包含以一已知速率充電之一電容器，其中當光子由光源102發射時開始充電，且當光子由陣列120接收時停止。

Where c is the speed of light, which is approximately equal to 3×10 ⁸ m/s, and T _TOF corresponds to the round trip time, which is the amount of time a pulse of light travels to and from the object shown in Figure 1. Therefore, once the round-trip time is known, the distance L can be calculated and then used to determine the depth information of the object 130. The controller 126 is coupled to a plurality of pixels 120 (including the first pixel 122, which can be coupled to a readout circuit to read out the charge and convert the charge to data indicating the charge) and the light source 102, and includes logic, which should be The execution causes the time-of-flight system 100 to perform operations for determining the round-trip time. The logic may include charging a capacitor at a known rate, where charging starts when photons are emitted by the light source 102 and stops when the photons are received by the array 120.

In some examples, the time-of-flight sensor 100 is included in a palm-sized device (eg, a mobile phone, a tablet computer, a camera, etc.) that has a size and power constraints based at least in part on the size of the device. Alternatively or in addition, the time-of-flight system 100 may have specific desired device parameters, such as frame rate, depth resolution, lateral resolution, and the like. In some examples, the time-of-flight sensor 100 is included in a LiDAR system.

FIG. 2A shows a part of the TOF sensor 200A of FIG. 1 according to the teachings of the present invention Part of an example circuit diagram. The circuit 200B is an equivalent circuit. As depicted, the circuit 200A includes a photodiode 203 (e.g., a single-photon avalanche photodiode (SPAD)), a first transfer transistor 205, a second transfer transistor 207, and a first floating diffusion 209 (e.g., a A doped well in the semiconductor material), the second floating diffusion 211 (for example, a doped well in the semiconductor material), and the inductor 213.

As shown, the first floating diffusion 209 is coupled to the photodiode 203 to receive the charge generated when the photodiode 203 receives one or more photons. The second floating diffusion 211 is similarly coupled to the photodiode 203 to receive electric charges. The first transfer transistor 205 is coupled to transfer the charge from the photodiode 203 to the first floating diffusion 209, and the second transfer transistor 207 is coupled to transfer the charge from the photodiode 203 to the second floating diffusion. In the diffuser 211. The inductor 213 is coupled between a first gate terminal of the first transfer transistor 205 and a second gate terminal of the second transfer transistor 207. In the depicted example, the inductor 213, the first gate terminal of the first transfer transistor 205, and the second gate terminal of the second transfer transistor 207 form a resonant circuit. Therefore, the inductor 213 applies a first oscillating voltage to the first gate terminal and a second oscillating voltage to the second gate terminal. The first oscillating voltage applied to the first gate terminal may be 180 degrees out of phase with the second oscillating voltage applied to the second gate terminal. As mentioned above, using an inductor to recycle the charge provided to the gate electrode of the transfer transistor can save a considerable amount of sensor power, because there can be thousands of photodiodes and transfer transistors per chip .

其中ω₀係振盪頻率，L係電感，且C₁及C₂分別係兩個電容器C(OX1)及C(OX2)之電容(其係兩個轉移閘之接面電容)。在各種實例中，上述變數之值可經設計使得振盪頻率可大於100MHz(例如250MHz)。 The circuit 200B equivalent to the circuit 200A when the first transfer transistor 205 and the second transfer transistor 207 are turned on at their respective times is also shown. The oscillation frequency ω _{0 of the} equivalent circuit is given by the equation:

Among them, ω ₀ is the oscillation frequency, L is the inductance, and C ₁ and C ₂ are the capacitances of the two capacitors C (OX1) and C (OX2) respectively (which are the junction capacitances of the two transfer gates). In various examples, the values of the aforementioned variables can be designed such that the oscillation frequency can be greater than 100 MHz (for example, 250 MHz).

FIG. 2B shows an example schematic diagram of a portion of the circuit diagram of FIG. 2A according to the teachings of the present invention. In the depicted example, the photodiode 203, the active region of the first transfer transistor 205, the active region of the second transfer transistor 207, the first floating diffusion 209, and the second floating diffusion 211 are disposed on the semiconductor material 201 (Such as silicon). The photodiode 201 is positioned in the semiconductor material 201 to absorb light and generate charges in response to the light.

As shown, the inductor 213 is disposed in a logic wafer (for example, containing one or more metal layers), and the logic wafer is coupled to a non-illuminated side of the semiconductor material 201. The inductor 213 may be coupled to the gate electrode, which has a bonding through hole extending from the logic wafer to the semiconductor material 201 through a bonding oxide. As shown, the inductor 213 may include a metal coil that is substantially flat, and the metal coils form a concentric substantially rectangular shape. However, in other examples, the metal coil may adopt other shapes, which are not necessarily rectangular, such as a circle, a hexagon, or the like. In addition, in some examples, metals (such as copper, aluminum, silver, or the like) may not include a single planar coil, but may include multiple coils in different planes in the logic wafer.

In an example, it is assumed that _Cox (TX) = 5×10 ^-8 F/cm ² (where the dielectric constant k = 4, the gate oxide thickness is approximately = 70 nm), and must be turned on/off at the same time (ie, turn on /Turn off) All transfer transistors (TX). Therefore, for a 400×250 transfer transistor array, each TX has a ^{size of 0.1 μm 2} , and the total capacitance is 5 pF. Therefore, in the depicted example, L needs to be 160nH to achieve a switching oscillation frequency of 250MHz between TX1 and TX2. However, those of ordinary skill who benefit from the present invention should understand that these parameters may vary depending on the device size and material selection.

FIG. 2C shows an example of the inductor of FIG. 2B according to the teachings of the present invention Schematic. In the depicted example, the inductor 213 includes a metal coil that is substantially flat (e.g., exists in a single plane in a cross-section of the device). As shown in the depicted example, the metal coil forms a concentric substantially rectangular shape and is a continuous coil. As shown in FIG. 2B, the inner end of the coil can be coupled to the gate of the first transfer transistor, and the outer end of the coil can be coupled to the gate of the second transfer transistor, or vice versa.

In the depicted example, assuming ~250MHz operation, D(OUT) can be 100μm, D(IN) can be 20.8μm, width can be less than 1μm (eg 0.4μm), interval can be less than 1μm (eg 0.4μm), and can be There are 25 or more turns (for example, 50 turns-the number of turns of the coil). Those skilled in the art who benefit from the present invention should understand that only a smaller number of turns are depicted for illustrative purposes, because more turns are redundant and not easy to illustrate.

The above description of the illustrated examples of the present invention, including the content described in the abstract, is not intended to be exhaustive or to limit the present invention to the precise form disclosed. Although specific examples of the present invention are described herein for the purpose of illustration, those familiar with the related art should realize that various modifications are possible within the scope of the present invention.

In view of the above detailed description, these modifications can be made to the present invention. The terms used in the scope of the attached application should not be construed as limiting the present invention to the specific examples disclosed in the specification. The fact is that the scope of the present invention will be determined entirely by the scope of the attached patent application, and the scope of the patent application shall be interpreted in accordance with the established principles for the interpretation of the scope of the patent application.

200A: TOF sensor/circuit

200B: Circuit

203: photodiode

205: The first transfer transistor

207: The second transfer transistor

209: The first floating diffusion

211: The second floating diffusion

213: Inductor

C(OX1): Capacitor

C(OX2): Capacitor

C1: Capacitance

C2: Capacitance

L: inductance

Claims (20)

A sensor including: A photodiode arranged in a semiconductor material to receive light and convert the light into electric charges; A first floating diffusion coupled to the photodiode to receive the charge; A second floating diffusion coupled to the photodiode to receive the charge; A first transfer transistor, which is coupled to transfer the charge from the photodiode to the first floating diffusion; A second transfer transistor coupled to transfer the charge from the photodiode to the second floating diffusion; and An inductor coupled between a first gate terminal of the first transfer transistor and a second gate terminal of the second transfer transistor, wherein the inductor, the first gate terminal and the second gate The terminals form a resonant circuit. The sensor of claim 1, wherein the inductor applies a first oscillating voltage to the first gate terminal and a second oscillating voltage to the second gate terminal, and wherein the inductor is applied to the first gate terminal The first oscillating voltage is 180 degrees out of phase with the second oscillating voltage applied to the second gate terminal. The sensor of claim 2, wherein the inductor applies the first oscillating voltage to the first gate terminal and the second oscillating voltage to the second gate terminal at a frequency greater than 100 MHz. The sensor of claim 1, wherein the inductor is disposed in a logic wafer coupled to a non-illuminated side of the semiconductor material. The sensor of claim 4, wherein the inductor includes a substantially flat metal coil. The sensor of claim 5, wherein the metal coil forms a concentric substantially rectangular shape. The sensor of claim 5, wherein the metal coil has an interval between windings less than 1 μm and a winding width less than 1 μm. Such as the sensor of claim 5, wherein the metal coil has 25 or more windings. Such as the sensor of claim 5, wherein the outer diameter of the metal coil is greater than 10 μm. Such as the sensor of claim 1, wherein the photodiode includes a single-photon sudden avalanche photodiode (SPAD). A time-of-flight (TOF) sensor system, which includes: A light emitter, which is coupled to emit light; and A plurality of pixels are arranged in a semiconductor material and arranged in an array to receive the light, wherein each pixel includes: A photodiode arranged in a semiconductor material to receive light and convert the light into electric charges; A first floating diffusion coupled to the photodiode to receive the charge; A second floating diffusion coupled to the photodiode to receive the charge; A first transfer transistor, which is coupled to transfer the charge from the photodiode to the first floating diffusion; A second transfer transistor coupled to transfer the charge from the photodiode to the second floating diffusion; and An inductor coupled between a first gate terminal of the first transfer transistor and a second gate terminal of the second transfer transistor, wherein the inductor, the first gate terminal and the second gate The terminals form a resonance circuit. For example, the TOF sensor system of claim 11, which further includes a readout circuit coupled to read out the charge from the first floating diffusion and the second floating diffusion and convert the charge into a representation Information about the charge. For example, the TOF sensor system of claim 12, which further includes a controller coupled to the readout circuit to receive the data, wherein the controller includes logic that, when executed by the controller, causes the The TOF sensor system performs the following operations: Emit the light from the light emitter; Receive the light with the photodiode; and Based on the data, a flight time of the light emitted from the light emitter traveling to an object and returning to an array is calculated. For example, the TOF sensor system of claim 13, wherein the controller further includes logic that, when executed by the controller, causes the system to perform operations including the following: A distance from the TOF sensor system to the object is calculated based on the flight time. For example, the TOF sensor system of claim 11, wherein the inductor applies a first oscillating voltage to the first gate terminal and a second oscillating voltage to the second gate terminal, and wherein the inductor is applied to the first gate terminal. The first oscillating voltage of the gate terminal and the second oscillating voltage applied to the second gate terminal are 180 degrees out of phase. Such as the TOF sensor system of claim 14, wherein the inductor applies the first oscillating voltage to the first gate terminal and the second oscillating voltage to the second gate terminal at a frequency greater than 100 MHz. The TOF sensor system of claim 11, wherein the inductor is disposed in a logic wafer coupled to a non-illuminated side of the semiconductor material. Such as the TOF sensor system of claim 17, wherein the inductor includes a substantially flat metal coil. Such as the TOF sensor system of claim 18, wherein the metal coil has 25 or more windings. Such as the TOF sensor system of claim 11, wherein the photodiode includes a single-photon sudden avalanche photodiode (SPAD).

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